Endoscope treatment tools which can be inserted into the channel of an endoscope are employed when performing per os treatments using an endoscope. The endoscope treatment tool has a flexible, long and narrow inserted part. A treatment part for carrying out the treatment is provided on the distal end of the inserted part which is inserted into the body. An operator portion for manipulating the treatment part is provided to the base end of the inserted part, which is pulled out on the hand-held side.
An injection syringe may be cited here as one example of an endoscope treatment tool and is used when injecting and infusing a medicinal liquid into a tissue. This injection syringe is a treatment part in which a hollow needle is passed in a freely advancing and retreating manner through a sheath, which serves as the inserted part, with the distal end of the hollow needle piercing the tissue. The operator portion includes a pipe-shaped operator portion main body which is fixed in place to the base end of the sheath, and a base which is attached in a freely advancing and retreating manner to the operator portion main body and is connected to the hollow needle. This type of injection syringe is introduced into the body in an arrangement in which the distal end of the hollow needle is housed within the sheath. When piercing the tissue, the base is pushed in relative to the operator portion main body, causing the distal end of the hollow needle to be projected out from the sheath.
The design of an operator portion for switching between projecting out and retracting back the hollow needle is disclosed, for example, in Patent Reference No. 1. In this operator portion, a vertically directed groove is provided to the operator portion main body, with the ends of the groove forming stopping seats which are expanded in an approximately circular shape. An operator tube which is inserted into the operator portion main body is connected to the base, and an elastic ligulate section extending in the vertical direction is provided to the operator tube. A pin is provided to the free end of the elastic ligulate section. This pin has a two-step design with differing diameters. The large diameter base portion is larger than the width of the groove on the operator portion main body side, but is smaller than the diameter of the stopping seats. The small diameter distal end portion is smaller than the width of the groove. The operator tube is inserted into the operator portion main body and is biased by means of a spring in the direction of retreating of the hollow needle.
When assembling the injection syringe, the operator tube is inserted into the operator portion main body until the pin reaches the front stopping seat. The elastic ligulate section reverts to its original state, and the pin enters the front stopping seat. At this time, the distal end of the hollow needle is located at its operating position, projecting out from the sheath. Once the treatment is concluded, the operator manually pushes in the pin. The compressed spring reverts to its original state and the operator tube and the base are pushed back. The distal end portion of the pin moves while being guided in the groove. Once the rear stopping seat is reached, the elastic ligulate section reverts to its original state, and the pin enters the rear stopping seat, causing the operator tube and base to stop. At this position, the distal end of the hollow needle is housed inside the sheath.
[Patent Document 1]                Published Japanese translation No. 2005-534436 of PCT International Publication        